Filling small dimension vias using supercritical carbon dioxide

ABSTRACT

Suitable particles may be deposited within an extremely small high-aspect ratio via by flowing the particles in a suspension using supercritical carbon dioxide. The particles may be made up of diblock copolymers or silesquioxane-based materials or oligomers of phobic homopolymers or pre-formed silica-based particles stabilized using diblock copolymers and may include chemical initiators to permit in situ polymerization within the via.

This is a divisional of prior Application No. 10/393,712, filed Mar. 21,2003 now U.S Pat. No. 6,812,132.

BACKGROUND

This invention relates to processes for making semiconductor integratedcircuits and, particularly, to techniques used for filling relativelysmall dimension vias.

In the process of forming dual damascene patterns, the back end of theline process of semiconductor manufacturing may use the via firstpatterning approach. In such a process, an interlayer dielectric may bepatterned with a relatively smaller-diameter via than the correspondingmetal/trench layer. An anti-reflective coating may then be used to fillthe via and to coat the interlayer dielectric for the subsequent trenchpattern (for lithographic concerns).

The via fill, generally, is obtained by the spin-coating of a solutionof a polymeric material in a solvent and an evaporation of the solventwith a solid material, filling the via in the interlayer dielectric.

As the dimensions of the via and the interconnects continue to shrinkwith ongoing advances in semiconductor lithography, the limit ofdimensions where the liquid is able to enter and fill the via is beingreached due to the high liquid viscosity of the polymeric or oligomericsolution. In other words, the viscosity of the solution is sufficient,even if very low, to prevent the complete filling of extremely finevias.

Further, the removal of the solvent through evaporation may also bedetrimental to the structure, due to the high capillary forces involved.The increase in the aspect ratio of the features makes entry of thesolutions into those features relatively difficult. In other words, whenthe via becomes sufficiently small, it is relatively hard to remove thesolvent from the structure due to capillary forces and to get thesolution into the structure because of capillary forces without damageto the features.

Thus, there is a need for better ways to fill relatively small dimensionvias in advanced semiconductor processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross-sectional view of one embodiment of thepresent invention at an early stage of manufacture;

FIG. 2 is an enlarged cross-sectional view of the embodiments shown inFIG. 1 at a subsequent stage of manufacture;

FIG. 3 is an enlarged cross-sectional view of still a subsequent stageof manufacture in accordance with one embodiment of the presentinvention;

FIG. 4 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 5 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 6 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 7 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;and

FIG. 8 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Supercritical carbon dioxide, with its low viscosity and low surfacetension, is capable of wetting virtually all surfaces and is able toenter and leave small sized features in interlayer dielectrics and otherstructures. Supercritical carbon dioxide is formed when carbon dioxideis heated above 31° C. at pressures above 1070 pounds per square inch.Further, the removal of supercritical carbon dioxide as a gas duringdepressurization that is devoid of any capillary forces leaves thefeatures intact.

Supercritical carbon dioxide may be used as a solvent for generation ofa suspension of particles/micelles of oligomeric species.

Certain monomers and oligomers are rich in fluorine and silicon.Examples of such monomers and oligomers include fluorocarbons andsiloxanes that are soluble in carbon dioxide due to favorable chemicalinteractions. A suspension of particles comprised of such monomers andoligomers may be created such that particles of varying dimensions onthe order of a few nanometers may be created. These particles may bestabilized using diblock copolymers, such as polystyrene-block-polyfluoromethyl methacrylate or polystyrene-block-polydimethyl siloxane,with a corona of the particle or micelle having favorable interactions,like fluorocarbons or siloxanes, and the core of the micelle withorganic content such as polystyrene. The diblock copolymers themselvesform particles in certain cases and they can also be used as stabilizersfor particles that are made of CO₂-phobic species like polystyrene, etc.(non-fluorinated/non-siloxane containing hydrocarbon oligomers).

The size of the micelle or particle can be controlled by the size of theblocks of a diblock copolymer, the carbon dioxide density, the chemicalmakeup of the side groups of the diblock copolymers or the degree ofcrosslinking of hydrogen silesquioxane or methyl-silesquioxane(HSQ-based or MSQ-based) silica particles.

As an example, the size of the particles may be from 5 nm to 40 nmdepending on the side groups of the diblock copolymers and molecularweights of the diblock copolymers. In one embodiment the size of theblocks of the diblock copolymer may be from 3-4 repeat units of theblocks of the diblock copolymer and the carbon dioxide density may befrom 0.1 to 1.0 gm/cc. The chemical makeup of the side groups of thediblock copolymers may be siloxane-based or fluoroacrylates as one ofthe diblocks and alykl or aromatic hydrocarbon-based as the other blockand also the use of other anti-solvents, liquid or supercritical (likeethane) for creation and stabilization of the particles in someembodiments.

The micelles may be suspended in supercritical carbon dioxide and may bemanipulated to fill a via due to gravity (in which case the tunabilityof carbon dioxide density is very useful) or other active forces, likeelectric fields, when appropriate molecules are used as the core of themicelle (particle). The particles may be drawn to the top surface of theinterlayer dielectric and can be swept away by flowing supercriticalcarbon dioxide. The ability to flow the supercritical carbon dioxide isfacilitated by its low viscosity.

Due to their high fluorine content, the particles can be envisioned tobe less adhesive in nature, maintaining their integrity and notchemically/physically attaching to the dielectric surface. Thesuspension can also be designed to contain chemical initiators likebenzoyl peroxide for initiating the polymerization of the particles, ata higher temperature, to prepare a continuous filling once the vias arefilled with the particles to be polymerized. After the vias are filledwith solid material, another film of an identical or similar chemicalnature may be spun coated from regular liquid solutions for creating asmooth top surface, if desired. Aromatic molecules that function as dyesfor the absorption of irradiated light used for developing photoresistscan also be incorporated through this process from thesuspension/dispersion in supercritical carbon dioxide to createessentially an antireflective coating for the subsequent patterning ofthe trenches in the dual damascene process.

Further, pre-formed sub-20 nm-sized particles can also be used in thistechnique to be displaced in the vias by flowing supercritical carbondioxide.

Referring to FIG. 1, a dielectric 10 may be formed with a via 12 whichmay be on the order of about 10 to about 45 nanometers in oneembodiment. The via 12 may be filled by pre-formed or in situ formedparticles 16 suspended in supercritical carbon dioxide within a chamber14 over the dielectric 10. The dielectric 10 may be formed over asupport structure 11 in some embodiments.

The particles 16, which may also be called micelles, may be allowed tosettle down into the via due to gravity or other forces as shown in FIG.3. The particles on top of the dielectric 10 may be swept away by theflowing supercritical carbon dioxide as shown in FIG. 4.

Referring to FIG. 5, the steps shown in FIGS. 2, 3, and 4 may berepeated until the via 12 is substantially filled with particles 16. Atthis point, the supercritical carbon dioxide flow may be terminated, andthe chamber 14 may be heated to polymerize or “fuse” the particles 16 toform the polymer material 18 shown in FIG. 6. A portion of the via 12still remains unfilled at this stage in some embodiments.

The steps shown in FIGS. 2-6 may be repeated until the via 12 iscompletely filled with the filled 18 as shown in FIG. 7. Thereafter, aspin coating of a solution 20 may be formed, if desired. The material 20may be of the same or different material than the particles 16 or thebulk material 18.

As a result, high-aspect ratio vias having a size less than 40nanometers may be filled from solutions or suspensions of polymers orsilica or other HSQ or MSQ-based material in supercritical carbondioxide. The relatively low surface tension and viscosity of thesupercritical carbon dioxide, as well as its excellent wetability,facilitates this process. The favorable interactions of fluorocarbonsand polydimethyl siloxane and small molecular dyes may be used to formanti-reflective coatings. In situ polymerization of monomers andoligomers in suspended particles in supercritical carbon dioxide arefeasible. Good control of particle size or particles suspended in thesupercritical carbon dioxide may be achieved.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A semiconductor structure comprising: an interlayer dielectric; a viacontained in said interlayer dielectric; and a plurality of particlessuspendable in supercritical carbon dioxide deposited in said via, saidparticles including fluorocarbon.
 2. The structure of claim 1 whereinsaid particles include monomers.
 3. The structure of claim 1 whereinsaid particles include oligomers.
 4. The structure of claim 1 whereinsaid particles include siloxanes.
 5. The structure of claim 2 whereinsaid particles arc stabilized using diblock copolymers.
 6. The structureat claim 1 including a dye in said via.
 7. The structure of claim 1wherein said via is less than about 45 nanometers.
 8. The structure ofclaim 1 wherein said particles include a polymerization initiator.
 9. Asemiconductor structure comprising: an interlayer dielectric; a viaformed in said interlayer dielectric; a plurality of particles depositedin said via, said particles including a polymerization initiator. 10.The structure of claim 9 wherein said particles are suspendable insupercritical carbon dioxide.
 11. The structure of claim 9 wherein saidparticles include monomers.
 12. The structure of claim 9 wherein saidparticles include oligomers.
 13. The structure of claim 9 wherein saidparticles include fluorocarbons.
 14. The structure of claim 10 whereinsaid particles are stabilized using diblock copolymers.
 15. Thestructure of claim 9 wherein said via is less than about 45 nanometers.